Android asynctask on listview

Question

所以我有一個問題在onPostExecute方法中填充listActivity。 SingleData的結果列表是正確的...然後我使用自定義適配器綁定到android.R.id.list ...

但它給了我錯誤...我真的不明白爲什麼... 所以這裏的適配器的代碼..：

private class RequestAdapter extends ArrayAdapter<SingleData> { 

    private int _resource; 
    private LayoutInflater _inflater; 
    private Context _context; 

    public RequestAdapter(Context context, int textViewResourceId, 
      List<SingleData> objects) { 
     super(context, textViewResourceId, objects); 
     _resource = textViewResourceId; 
     _context = context; 
     _inflater = LayoutInflater.from(_context); 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 

     convertView = (ListView)_inflater.inflate(_resource,null); 
     SingleData sdd = getItem(position); 

     ImageView iv = (ImageView)convertView.findViewById(R.id.imagePlaceHolder_IV); 
     iv.setImageBitmap(sdd.thumbIMG); 

     TextView tv = (TextView)convertView.findViewById(R.id.createdAt_TV); 
     tv.setText(sdd.timeStamp); 

     // TODO Auto-generated method stub 
     return convertView;   
    } 

} 

這裏是onPostExecute：

private class DownloadTheImages extends AsyncTask<Void, Void, List<SingleData>> { 

    private Context _ctx; 

    public DownloadTheImages(Context ctx) { 
     _ctx = ctx; 
    } 

    protected void onPostExecute(List<SingleData> result) {    

     ListView mainLV = (ListView)findViewById(android.R.id.list); 
     mainLV.setAdapter(new RequestAdapter(_ctx, R.layout.single_row, result)); 

    } 

    protected List<SingleData> doInBackground(Void... params) { 
       ..... 
      .... 
       } 
     } 

和logcat的：

？

任何線索......感謝..

這些都是較新的錯誤：

10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.widget.AbsListView.obtainView(AbsListView.java:1430) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.widget.ListView.makeAndAddView(ListView.java:1745) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.widget.ListView.fillDown(ListView.java:670) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.widget.ListView.fillFromTop(ListView.java:727) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.widget.ListView.layoutChildren(ListView.java:1598) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.widget.AbsListView.onLayout(AbsListView.java:1260) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.view.View.layout(View.java:7175) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.widget.FrameLayout.onLayout(FrameLayout.java:338) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.view.View.layout(View.java:7175) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1254) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1130) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.widget.LinearLayout.onLayout(LinearLayout.java:1047) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.view.View.layout(View.java:7175) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.widget.FrameLayout.onLayout(FrameLayout.java:338) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.view.View.layout(View.java:7175) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.view.ViewRoot.performTraversals(ViewRoot.java:1140) 
10-20 16:32:56.615: E/AndroidRuntime(1487):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1859) 

Answer 1

這些行導致此問題。

 RequestAdapter adapter; // This will be member variable 
    ListView mainLV = (ListView)findViewById(android.R.id.list); 
    mainLV.setAdapter(new RequestAdapter(_ctx, R.layout.single_row, result)); 

移動這些線中的onCreate（）和實例適配器然後，在簡單地onPostExecute值添加到「結果」 ArrayList和調用adapter.notifyDatasetChanged（）之前初始化的結果。避免在onPostExecute（）或onProgressUpdate（）中查找視圖。

Answer 2

我明白onPostExecute的工作方式是它接受從doInBackground（）傳入的結果對象。因此，除非您將此結果返回到doinbackground，然後將其傳遞到您的RequestAdapter，否則您將獲得NullPointer。你在哪裏初始化你的結果成員？在OnCreate？

protected List<SingleData> doInBackground(Void... reuslt) { 
      ..... 
     .... 
     ///Do some stuff 

      return result; 
      } 
    } 


private class DownloadTheImages extends AsyncTask<Void, Void, List<SingleData>> { 

private Context _ctx; 

public DownloadTheImages(Context ctx) { 
    _ctx = ctx; 
}